(1) Field of the Invention
The present invention relates to a connecting rod bearing for an internal combustion engine that is configured so that lubrication oil supplied to an inner circumferential surface of a main bearing supporting a crankshaft is supplied to an inner surface of a connecting rod bearing supporting a crankpin portion through an internal lubrication oil path of the crankshaft.
(2) Description of Related Art
A crankshaft of an internal combustion engine is supported at a journal section thereof in a cylinder block lower portion of the internal combustion engine via a main bearing constituted by a pair of half bearings. For the main bearing, lubrication oil which is discharged by an oil pump through a through-hole formed in a wall of the main bearing from an oil gallery formed in a cylinder block wall is fed into a lubrication oil groove formed along an inner circumferential surface of the main bearing. Further, a first lubrication oil path is formed to penetrate the journal section in a diameter direction thereof, so that both end openings of the first lubrication oil path communicate with the lubrication oil groove of the main bearing. Further, a second lubrication oil path passing through a crank arm section is formed to branch from the first lubrication oil path of the journal section, and the second lubrication oil path communicates with a third lubrication oil path formed to penetrate a crankpin in a diameter direction thereof. The lubrication oil fed into the lubrication oil groove formed in the inner circumferential surface of the main bearing through the through-hole from the oil gallery in the cylinder block wall in this manner passes through the first lubrication oil path, the second lubrication oil path and the third lubrication oil path, and is supplied from a discharge port opened at a tail end of the third lubrication oil path to a gap between sliding surfaces of the crankpin and the connecting rod bearing (for example, see JP-A-08-277831).
The lubrication oil fed to the connecting rod bearing through the journal section of the crankshaft from the cylinder block of the internal combustion engine is likely to be accompanied by foreign matters existing in the lubrication oil paths of respective sections. The foreign matters may damage the sliding surface of the connecting rod bearing, if the foreign matters accompany the lubrication oil and are fed to the gap between the sliding surfaces of the crankpin and the connecting rod bearing. Accordingly, the foreign matters entering the gap between the sliding surfaces of the crankpin and the connecting rod bearing need to be quickly discharged to an outside from a sliding surface portion.
Conventionally, as a main bearing and a connecting rod bearing, sliding bearings each composed of a pair of half bearings have been adopted. In the sliding bearing, so-called crush reliefs are formed adjacently to contact surfaces of the half bearings.
A crush relief is a wall thickness-reduced region, which is formed so that a wall thickness of a region adjacent to a circumferential end surface of the half bearing decreases toward the circumferential end surface. The crush reliefs are formed with the objective of absorbing positional displacement and deformation of butting surfaces of the half bearings when the pair of half bearings are assembled (for example, see JP-A-04-219521).
Further, in some cases, a plurality of circumferential grooves which continuously extend in the circumferential directions are formed on inner circumferential surfaces of half bearings constituting a sliding bearing. Such circumferential grooves are formed generally for enhancing oil retainability of lubricating oil in the inner circumferential surface of the half bearing.
Foreign matters sometimes get mixed into the lubricating oil, and the foreign matters which are released to an inner circumferential surface of the connecting rod bearing are readily discharged into a relief gap from the lubricating oil path of the crankpin surface. Some of the discharged foreign matters are discharged to the outside from both end portions in the width direction of the relief gap, but other foreign matters remain and flow to the crankpin rotation forward side by accompanying the crankpin surface.
In the crush relief on the rear side in the crankpin rotational direction, the relief gap gradually becomes narrower toward the front side in the rotational direction. Therefore, the foreign matters contact the crankshaft surface at a portion where the relief gap is narrow, and are forced into the relief surface which is narrowed. The foreign matters forced therein are caught by an inner side surface (edge portion) of the discharge port when the discharge port on the crankpin surface passes, and are dragged to the inner circumferential surface side of the half bearing to cause the problem of damaging the circumferential surface easily.
As a measures dealing with the foreign matters getting mixed into the lubricating oil in a half bearing for a crankshaft of an internal combustion engine in which crush reliefs are formed at both circumferential end portions of the inner circumferential surface, there is the proposal of forming an axial groove at least in a position adjacent to the crush relief formed in the circumferential end portion of the inner circumferential surface of the half bearing located on the rear side in the relative rotational direction of the crankshaft, and to the inner circumferential surface of the half bearing. The axial groove is formed throughout an entire region in the width direction of the inner circumferential surface of the half bearing, and therefore, the foreign matters can be discharged to an outside of the bearing together with the lubricating oil by the axial groove (for example, see JP-A-2012-002247).
When the bearing of JP-A-2012-002247 is applied to the connecting rod bearing for a crankpin of a crankshaft of an internal combustion engine, entry of foreign matters into the inner circumferential surface of a half bearing hardly occurs, but during the operation time of the internal combustion engine, oil leakage to the outside of the bearing from the axial groove is always involved. In the internal combustion engines in which the oil pumps are miniaturized, and the supply amounts of the lubricating oil to the bearings are decreased in recent years, the problem that the oil supply amount to the inner circumferential surface decreases sometimes arises, in the case of the half bearings of JP-A-2012-002247.